It is common practice in installing conduit for housing, electrical, telephone, and other lines to assemble the conduit, which in some cases is placed underground, and when the conduit has been finally assembled to send a carrier device through the conduit leading a messenger line which may then be attached to the appropriate electrical line which can be drawn through the conduit.
Examples of line-pulling carriers in use today are shown in U.S. patent Ser. No. 3,119,600, Bitter, and U.S. patent Ser. No. 3,246,878, Hamrick. The line-pulling carrier is made of a flexible, spongy material so that, theoretically, it may move over water or accumulated debris in the conduit, and also go around curves and bends and be flexible enough so that when it passes indentations in the conduit its movement is not impeded.
In practice, however, these devices often will stick and cause great difficulty in threading electrical materials through conduit.
Earlier devices utilized flexible materials which could be blown through a conduit such as in U.S. patent Ser. No. 1,033,587, Hodgman, and U.S. patent Ser. No. 382,257, Geyser. Both of these disclosures involve the use of a relatively stiff member.
In the case of Hodgman, its item 1, a flexible band 10 is holding the material in a position against the inner wall of the conduit.
In the case of Geyser, there is a shaft 2 which is rigid.
Neither of these devices would permit the carrier to go around bends in the conduit because of the rigid shafts and U.S. patent Ser. No. 1,033,587, Hodgman, would have a great deal of friction on the interior of the shaft which would limit the length of conduit through which it could traverse.
Also in the prior art is U.S. patent Ser. No. 1,851,435, Jessup, which at 15 discloses a cone and a truncated cone connected together at their bases or connected at their bases to a small cylindrical portion. The messenger line is attached to the truncated portion below the base of the cones. Because of the shape of this device, it would tend to collapse when it met an obstacle with the result that it would not continue to pull the messenger through the conduit.